Water-dilutable coating compositions

ABSTRACT

The present invention relates to a water-thinnable coating composition comprising binders, inorganic pigments, and, if desired, organic pigments and also further customary additives such as solvents, fillers, plasticizers, stabilizers, wetting agents, dispersing auxiliaries, levelling agents, defoamers, catalysts and also further additives, individually or in a mixture with one another, and comprises at least one phosphoric ester and at least one fatty alcohol alkoxylate.

The invention relates to water-dilutable coating compositions comprisingbinders, aluminum pigment, and an aqueous diluent.

Water-thinnable coating compositions comprising binders, aluminumpigment and an aqueous diluent are known and are intended for use inparticular in the finishing of automobiles, for producing metalliccoating systems.

Metallic coating systems are nowadays applied preferably by theso-called basecoat/clearcoat technique, in which a basecoat pigmentedwith aluminum pigments is applied first and then coated over with aclearcoat.

A particular problem of aqueous coating compositions for producingmetallic coating systems is that they often have a pH which is so highthat the aluminum pigments used react with water, forming hydrogen. Thisphenomenon results in a range of problems, especially when the coatingmaterials are stored in closed containers.

A range of processes have been disclosed by means of which aluminumpigments are to be passivated in such a way (cf. e.g. EP-A-0581235) thatno hydrogen at all, or only a very small amount, is evolved. All ofthese processes, however, have the disadvantage that the gassingstability is still not satisfactory. With the use of known aluminumpigments passivated by chromation, it is necessary to accept impairmentsin the shade and metallic effect (flop) of the metallic coating systems.

The object on which the present invention is based is to provide awater-dilutable coating composition comprising binders, inorganic and,if desired, organic pigments and also further customary additives suchas solvents, fillers, plasticizers, stabilizers, wetting agents,dispersing auxiliaries, levelling agents, defoamers, catalysts andfurther additives, individually or in a mixture with one another, whichdo not have the aforementioned disadvantages of the prior art.

This object is achieved in accordance with the invention by said coatingcomposition comprising at least one phosphoric ester and at least onefatty alcohol alkoxylate.

The water-dilutable coating compositions of the invention can inprinciple comprise all binders suitable for water-dilutable coatingcompositions.

Binders which can be used include, accordingly, both refined naturalproducts, examples being products of rosin and oils or cellulosenitrates, and resins whose composition is entirely synthetic. The latterincludes phenolic resins, amine resins (e.g., urea resins, melamineresins), alkyd resins, polyvinyl acetates, epoxy resins, polyurethaneresins, polyester resins, rosin-modified phenolic resins, chlorinatedrubbers, chlorinated polypropylene, cyclorubbers, ketone resins, andacrylate resins.

Binders used in particular are water-dilutable or water-dispersiblepolyurethane resins, polyacrylate resins, polyester resins and aminoresins, which can be prepared in organic solution, and also mixturesthereof.

The polyurethane resins which can be used as binders are known inprinciple. Suitable examples are the polyurethane resins described inthe literature for use in water-based coating materials, provided thesepolyurethane resins—in a modification of the preparation described inthe respective literature—can be prepared in the form of organicsolutions.

Examples of suitable polyurethane resins are the resins described in thefollowing documents: EP-A-355433, DE-A 3545618, DE-A 3813866, and the asyet unpublished German Patent Application DE 4005961.8. For furtherdetails of the preparation of the polyurethane resins and examples ofsuitable compounds, therefore, reference may be made to these documents.

The polyacrylate resins used as binders are likewise known and aredescribed, for example, in DE-A 3832826. Suitable resins are generalwater-thinnable or water-dispersible polyacrylate resins which can beprepared in the form of organic solutions.

Also suitable as binders are water-dilutable or water-dispersiblepolyester resins which can be prepared in the form of organic solutions.Use is made, for example, of corresponding commercially customarywater-dilutable or water-dispersible polyester resins, and also thepolyester resins commonly used in water-based coating materials.

Further suitable binders include water-dilutable or water-dispersibleamino resins. Preference is given to the use of water-dilutable melamineresins. These are, generally, etherified melamine formaldehydecondensates.

Apart from the degree of condensation, which should be as low aspossible, the water-solubility of the amino resins depends on theetherifying component, with only the lowest members of the alcohol orethylene glycol monoether series giving water-soluble condensates. Thegreatest importance is possessed by the methanol-etherified melamineresins. With the use of solubilizers, butanol-etherified melamine resinscan also be dispersed in an aqueous phase. A further possibility is toinsert carboxyl groups into the condensate. Transetherification productsof highly etherified formaldehyde condensates with oxycarboxylic acidsare soluble in water following neutralization, by way of their carboxylgroups, and may be present in the base paints.

As binders it is of course also possible to use mixtures of theaforementioned binders and, in addition or alone, other water-dilutableor water-dispersible binders.

The coating compositions of the invention can comprise customaryadditives such as solvents, plasticizers, stabilizers, wetting agents,rheological auxiliaries, dispersing auxiliaries, levelling agents,defoamers and catalysts, and also additives individually or in a mixturein the customary amounts. These substances can be added to theindividual components and/or to the mixture as a whole.

The coating compositions of the invention can comprise, besides water,the customary solvents, examples being aliphatic or aromatichydrocarbons, mono- or polyhydric alcohols, ethers, ethers, glycolethers and esters thereof, and ketones, such as for example, toluene,xylene, butanol, ethyl glycol or butyl glycol (=ethylene glycolmonoethyl or monobutyl ether) and acetates thereof, butyldiglycol(ethylene glycol dibutyl ether), ethylene glycol dimethyl ether,diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone,acetone, isophorone, or mixtures thereof.

Further components which may be added to the basecoats of the inventioninclude crosslinked polymeric microparticles, as are disclosed, forexample in EP-A-38 127, and/or customary organic or inorganic additives.For instance, examples of effective thickeners are sheet silicates,water-soluble cellulose ethers, such as hydroxyethyl cellulose, methylcellulose or carboxymethyl cellulose, and also synthetic polymers havingionic and/or associative groups, such as polyvinyl alcohol,poly(meth)acrylic acid, polyvinyl pyrrolidone, styrene maleic anhydrideor ethylene maleic anhydride copolymers and their derivatives, or elsehydrophobically modified ethoxylated piperidine and triethanolamine.Particular preference is given to the use of tertiary amines asneutralizing agents, especially dimethylethanolamine, triethylamine,tripropylamine and tributylamine.

The basecoat compositions of the invention can comprise all of the dyesor pigments which are known and are customary in the coatings industry.

Examples of dyes and pigments, which can be organic or inorganic innature, are titanium dioxide, graphite, carbon black, zinc chromate,strontium chromate, barium chromate, lead chromate, lead cyanamide, leadsilicochromate, zinc oxide, cadmium sulfide, chromium oxide, zincsulfide, nickel titanium yellow, chromium titanium yellow, iron oxidered, iron oxide black, ultramarine blue, phthalocyanine complexes,naphthol red, quinacridones, halogenated thioindigo pigments or thelike.

Particularly preferred pigments are metal powders, individually or in amixture, such as copper, copper alloys, aluminum and steel, preferablyaluminum powders, which are used in at least predominant proportion and,specifically, in an amount of from 0.5 to 25% by weight based on theoverall solids content of the binders in the coating compositions. Alsosuitable are customary commercial pearl lustre pigments. It is alsopossible to conceive of the use of combinations with transparent metaloxide, e.g. iron oxide red, titanium dioxide. Metallic pigments used arecommercially customary untreated metal powders and also those which havebeen specially pretreated for aqueous systems.

The metal powders can also be used together with one or more of theabovementioned nonmetallic pigments or dyes. In this case the proportionthereof is chosen such that the desired metallic effect is notsuppressed.

Furthermore, the coating composition of the invention comprises estersof phosphoric acid with alcohols or phenols. Aryl esters, alkyl estersand mixed phosphoric esters are used, as are phosphoric acidderivatives. Examples of suitable phosphoric acid derivatives are knownfrom EP-A-0581235.

It has now been found that the stabilisation of metal pigments,especially aluminum pigments, can be further substantially improved, andthus that it is possible to obtain a long-term protective effect for themetal pigments in aqueous and nonaqueous coating formulations, evenunder extreme conditions, if the phosphoric esters are used in a mixturewith fatty alcohol alkoxylates. In particular, the gassing stability isincreased by means of this measure.

Preference is given in accordance with the invention to the use ofethers formed by polyaddition of ethylene oxide; that is, by insertionof one or more —CH₂—CH₂—O groups in conjunction with an acidic oxygenatom with the aid of ethylene oxide. Suitable substrates are fattyalcohols, alkyl phenols, fatty amines, fatty acids and their amides,fatty acid esters, mercaptans and imidazolines.

The products of the reactions, which are carried out industrially underpressure (from about 1 to 5 bar) at temperatures from 120 to 220° C.,are linear ethers or polyethers which carry a hydroxyl group at onechain end and a functional group, which is dependent on the startingmaterial, at the other end. The addition of a defined amount of ethyleneoxide onto the substrate yields a distribution of homologousethoxylates, the width of which can be influenced in particular throughthe choice of catalyst.

It is common to use alkaline catalysts, especially sodium methoxide,which lead to a wide Schulz-Flory homolog distribution, whereas alkalineearth metal salts (e.g., calcium acetate, strontium phenoxide) induce anarrowing in accordance with a Poisson distribution. Acidic catalysts(for example, antimony pentachloride) likewise bring about a distinctnarrowing in the homolog distribution.

Particular preference is given in accordance with the invention to theethoxylates, derived from fatty alcohols, of the general formulaRO—(CH₂—CH₂—O)_(n)—H where n=4-10. The compounds used with preferenceinclude the fatty alcohol polyglycol ethers. In addition,alkylphenolpolyglycol ethers are also used.

In accordance with the invention, the phosphoric esters and the fattyalcohol alkoxylates are used in a mixture with one another. Theproportion of the mixture is 1-20% by weight, preferably 1-10% byweight, based on the solids content of the pigment to be stabilized. Thedensity of the mixture is 1.02 g/cm³ and its viscosity is 400 mPas.

A mixture of the invention composed of phosphoric ester and fattyalcohol alkoxylate contains preferably 2-98% by weight of phosphoricester and 2-98% by weight of fatty alcohol alkoxylate, it beingpossible, optionally, for customary organic solvents, and substancesother than the phosphoric ester and fatty alcohol alkoxylate, acting asadditives or coating components to be present. It goes without sayingthat the proportions of the above mixture of the invention always add upto 100% by weight. The mixture contains preferably 20-80% by weight,most preferably 40-60% by weight, for example 50% by weight, ofphosphoric ester. Irrespective of this, the fatty alcohol alkoxylate canbe present in proportions of preferably 20-80% by weight, mostpreferably 40-60% by weight, for example 50% by weight. It is preferredif the above mixture is free from the optional components.

The mixture comprising effect pigment, phosphoric ester and fattyalcohol alkoxylate is mixed with the above-described binders, coatingauxiliaries, fillers and pigments. First of all the metal slurry isprepared, by introducing bronze and 50% of the solvent used in theslurry as an initial charge and then adding the stabilizer, theremaining 50% of the solvent, then the binder and, finally, theneutralizing agent. This is mixed with the metallic coating.Surprisingly it has been found that the gassing stability issignificantly improved, especially when this mode of preparation isfollowed. Likewise, oxidation phenomena on the surface of the metalpigments are prevented. The graying of the pigment surfaces which isotherwise commonly observed, and the loss of brightness, is no longerobserved with the additives of the invention.

In addition to the additives of the invention it is also possible to addfurther substances which serve for passivation. One example is aluminiumpigments obtained by having passivated a lubricant-coated aluminumpigment in an aqueous passivating solution containing chromic acid and awater-soluble glycol ether of the general formula R¹(—O—CHR²—CH₂)_(n) OH(R¹ is a lower alkyl radical, R² is either a hydrogen atom or a loweralkyl radical, preferably a —CH₃ group, n is a number from 1 to 5)and/or a water-soluble glycol of the general formulaHO—(CHR³—CH₂—O—)_(n) H (R³ is either a hydrogen atom or a lower alkylradical, preferably a —CH₃ group, n is a number from 1 to 5) at least50° C., preferably from 60 to 90° C., with particular preference about80° C.

In order to obtain pigments having the desired properties, it isnecessary to use pigments which have a certain minimum lubricantcontent. The lubricant content is preferably established in the courseof the production process of the aluminum pigments.

Aluminum pigments coated with fatty amines as the lubricant result inpassivated pigments which have especially advantageous properties. Byfatty amines are meant mixtures of long-chain, predominantly primaryalkyl amines, which have been obtained, for example, from fatty acids byway of the associated nitrites by means of reduction.

As the lubricant-coated aluminum pigments it is possible to use commonlyknown and customary aluminum pigments consisting of aluminum or aluminumalloys, preferably of pure aluminum. Preference is given to the use ofaluminum pigments in flake form. The aluminum pigments can be used inthe form of the commercially available pastes without furtherpretreatment.

The passivation of the lubricant-coated aluminium pigments is conductedat at least 50° C., preferably from 60 to 90° C., with particularpreference about 80° C., in an aqueous solution which comprises chromicacid and a water-soluble glycol ether of the general formulaR¹(—O—CHR²—CH₂)_(n) OH (R¹ is a lower alkyl radical, R² is either ahydrogen atom or a lower alkyl radical, preferably a —CH₃ group, n is anumber from 1 to 5) and/or a water-soluble glycol of the general formulaHO—(CHR³—CH₂—O—)_(n) H (R³ is either a hydrogen atom or a lower alkylradical, preferably a —CH₃ group, n is a number from 1 to 5).

The aqueous solution may additionally include further additives whichhave a positive influence on the chromation process, such as, forexample, fluorides or phosphates.

Particularly good results are obtained if the passivating solutioncontains chromic acid and n-butyl glycol (CH₃—(CH₂)₃—O—CH₂—CH₂—OH).

Both the concentration of chromic acid and the concentration of glycolor glycol ether can be varied within wide limits. The passivatingsolution of the invention generally contains at least 1.5, preferablyfrom 1.5 to 4.0, with particular preference from 2.0% by weight ofchromic acid and from 3 to 30, preferably from 7 to 15, with particularpreference 10% by weight of water-soluble glycol ether and/orwater-soluble glycol.

The passivation is preferably conducted in the freshly preparedpassivating solution and is concluded in general after from 10 to 30minutes.

Following the end of passivation, the passivated pigment obtained isseparated from the passivating solution and washed thoroughly withwater. The passivated aluminum pigment thus obtained can then beincorporated into water-dilutable coating compositions in accordancewith methods which are common knowledge.

The water-dilutable coating compositions of the invention are preferablyused as basecoat compositions for producing basecoat/clearcoat metalliccoating systems. They display excellent stability with respect tohydrogen evolution, and yield metallic coating systems which arecomparable in terms of their visual (flop, shade) and technological(moisture insensitivity, condensation resistance, intercoat adhesion)properties, with coating systems produced using conventional (i.e.,containing exclusively organic solvents as diluents) basecoatcompositions.

The applicability of the coating compositions of the invention is notrestricted to the finishing of automobiles. It is also possible to coatother substrates consisting of untreated or pretreated metal, wood,plastic or the like in a one-coat or multicoat process.

The PH of the coating composition can be from 7.5 to 8.5.

The invention is illustrated below with reference to the examples.

Unstabilized bronzes were investigated with and without the addition ofmixtures of phosphoric esters and fatty alcohol alkoxylates. Degressalwas used as a mixture with the substances used in accordance with theinvention. From the following table it is event that, in the case of usewithout the addition of Degressal, outgassing occurs after only one day.In contrast, the addition of Degressal had the effect of a markedreduction in the gassing instability.

Unstabilized aluminum bronzes 1 day 1 week 3 weeks Alpate 8160 outgassedAlpate 8160 + 2.5% 12.2 ml 11.8 ml Degressal SNC Alpate 8160 + 5.0% 6.2ml 11.3 ml Degressal SNC Alpate 8160 + 10.0% 10.0 ml 11.0 ml DegressalSNC Metallux 2156 outgassed Metallux 2156 + 2.5% 4.8 ml 10.2 mlDegressal SNC Metallux 2156 + 5.0% 1.8 ml 9.2 ml Degressal SNC Metallux2156 + 10.0% 0.0 ml 9.2 ml Degressal SNC Alpate 8160 + outgassedSicotransrot Alpate 8160 + 0.5 ml 7.2 ml Sicotransrot + 16.6% DegressalMetallux 2156 + outgassed Sicotransrot Metallux 2156 + 3.5 ml 10.0 mlSicotransrot + 16.6% Degressal

The Alpate products are aluminum pigments available through the companyToyal.

The Metallux products are alluminum pigments obtainable through thecompany Eckart.

Sicotransrot is an iron oxide pigment and Degrassal is a phosphoricester with a fatty alcohol alkoxylate and both are products from BASFAG.

Independently of the specific examples and embodiments described above,the following is noted in addition.

In the context of the invention, the expression metal pigments definesall kinds of pigments which have surfaces which in whole or in partcontain metal, these metal-containing surfaces exhibiting a tendency toform gas, especially hydrogen, on contact with water and at pH levelstypical of coating compositions. The surfaces in question comprise, inthe majority of cases, metal present in elemental form, or metalcompound structures which have not been adequately passivated. Metalpigments can be effect pigments, i.e., pigments which in addition to orinstead of a purely coloring effect induce optical effects which differfrom this. Metal pigments of this kind are also called metallic or metaleffect pigments. Alternatively, however, metal pigments may have anexclusively coloring effect or may be transparent.

What is claimed is:
 1. A water-dilutable coating composition comprisingat least one binder, at least one inorganic pigment other than a metalpigment, at least one metal pigment, at least one phosphoric ester, andat least one fatty alcohol alkoxylate, and optionally, a compoundselected from the group consisting of organic pigments, solvents,fillers, plasticizers, stabilizers, wetting agents, dispersingauxiliaries, leveling agents, defoamers, catalysts and mixtures thereof;wherein the at least one metal pigment has been passivated.
 2. Awater-dilutable coating composition as claimed in claim 1, obtained byadding a mixture comprising the at least one inorganic pigment otherthan a metal pigment, the at least one metal pigment, the at least onephosphoric ester, and the at least one fatty alcohol alkoxylate to theat least one binder.
 3. A water-dilutable coating composition as claimedin claim 1 comprising metal phosphoric acid esters.
 4. A water-dilutablecoating composition as claimed in claim 3, comprising aluminumphosphoric acid esters.
 5. A water-dilutable coating composition asclaimed in claim 1, wherein the proportion of phosphoric ester and offatty alcohol alkoxylate together is from 1 to 20% by weight based onthe solids content of the pigment to be stabilized in the mixture.
 6. Awater-dilutable coating composition as claimed in claim 5, wherein theproportion of phosphoric ester and of fatty alcohol alkoxylate togetheris 1-10% by weight.
 7. A water-dilutable coating composition as claimedin claim 1 wherein the at least one metal pigment comprises at least onemetal powder as an effect pigment.
 8. A water-dilutable coatingcomposition as claimed in claim 1, wherein the at least one metalpigment comprises as an effect pigment a compound selected from thegroup consisting of copper alloys, aluminum, steel, pearl lustrepigments, and mixtures thereof.
 9. A water-dilutable coating compositionas claimed in claim 1 wherein said fatty alcohol alkoxylates areethoxylates.
 10. A water-dilutable coating composition as claimed inclaim 1, wherein the at least one phosphoric ester, and the at least onefatty alcohol alkoxylate are added to the coating composition as amixture, and wherein the mixture has a density of 1.02 g/cm³ and aviscosity of 400 mPas.
 11. A water-dilutable coating composition asclaimed in claim 1, wherein the pH is from 7.5 to 8.5.
 12. A process forpreparing a water-dilutable coating composition as claimed in claim 1comprising preparing a dispersion comprising the at least one metalpigment, the at least one inorganic pigment other than a metal pigment,the phosphoric ester, and the fatty alcohol alkoxylate and then mixingthe dispersion with the binder and optionally the compound selected fromthe group consisting of organic pigments, solvents, fillers,plasticizers, stabilizers, wetting agents, dispersing auxiliaries,levelling agents, defoamers, catalysts, and mixtures thereof.
 13. Awater-dilutable coating composition as claimed in claim 1, wherein thecoating composition can be applied to a metal substrate.